(2018-08-08, 13:22)Hitcher Wrote: If the skin doesn't have it then you can't use it.
Yes you can. Though all skins include font ttf files in /fonts, this is not necessary. See the wiki. Any font referenced by name in <skin.name>/xml/Font.xml can be used, provided the respective font ttf file is put in ./kodi/media/fonts and named exactly as referenced in <skin.name>/xml/Font.xml.
(NOTE: You must take care to name the font correctly in Font.xml. If you don't hand-edit the naming the numerical string provided in idloc="" takes precedence, reading its value from <skin.name>/languages/<...>/strings.po, which of course is a value having nothing to do with your custom font.)
IMHO the wiki should also state that centralizing fonts is the correct approach, and that the current practice of including in every single font the exact same font(s) (Roboto, Roboto-Bold, Ubuntu/Ubuntu-M, Arial, etc) is inefficient, impedes maintenance, and should be dropped.
Come to think of it, the same approach should govern backgrounds. It makes little sense to duplicate the exact same SKINDEFAULT.jpg, mediaoverlay.jpg, tv.jpg etc in each and every skin you use, rather then centralize them all in .kodi/media.
Perhaps the biggest benefit of centralization of your fonts & backgrounds is that nothing gets lost upon a skin upgrade. The skins reside in the folder .kodi/addons; any change in them doesn't affect the folder .kodi/media.